The invention relates to a device for modifying the control times of gas-exchange valves of an internal combustion engine with a drive wheel in driven connection with a crankshaft and with a swashplate drive, which has at least one housing and a driven element in driving connection with a camshaft, wherein the housing and the driven element define a ring-shaped hollow space.
In internal combustion engines, camshafts are used for actuating the gas-exchange valves. Camshafts are mounted in the internal combustion engine such that cams mounted on these camshafts contact cam followers, for example, cup tappets, rocker arms, or finger levers. If the camshaft is set in rotation, then the cams roll on the cam followers, which in turn actuate the gas-exchange valves. Thus, both the opening period and also the amplitude, but also the opening and closing times of the gas-exchange valves, are set by the position and the shape of the cams.
Modern engine concepts allow variable valve train designs. On one hand, the valve lift and valve opening period should be made variable up to complete shutdown of individual cylinders. For this purpose, concepts such as switchable cam followers, variable valve trains, or electrohydraulic or electrical valve actuators are provided. Furthermore, it has been shown to be advantageous to be able to influence the opening and closing times of the gas-exchange valves during the operation of the internal combustion engine. It is likewise desirable to be able to influence the opening or closing times of the intake or exhaust valves separately, in order, for example, to be able to selectively set a defined valve overlap. By setting the opening or closing times of the gas-exchange valves depending on the current engine-map range, for example, the current rotational speed or the current load, the specific fuel consumption can be lowered, which has a positive effect on the exhaust-gas behavior and increases the engine efficiency, the maximum torque, and the maximum output.
The described variability in the gas-exchange valve time control is implemented through a relative change of the phase position of the camshaft relative to the crankshaft. Here, the camshaft is usually in a driven connection with the crankshaft via a chain drive, belt drive, gearwheel drive, or equivalent drive concepts. Between the chain drive, belt drive, or gearwheel drive driven by the crankshaft and the camshaft there is a camshaft adjuster, which transmits the torque from the crankshaft to the camshaft. Here, this device for modifying the control times of the internal combustion engine is constructed such that during the operation of the internal combustion engine, the phase position between the crankshaft and camshaft is held reliably and, if desired, the camshaft can be rotated within a certain angular range relative to the crankshaft.
In internal combustion engines with separate camshafts for the intake and exhaust valves, these can each be equipped with a camshaft adjuster. Therefore, the opening and closing times of the intake and exhaust gas-exchange valves can be shifted in time relative to each other and the valve overlaps are set selectively.
The location of modern camshaft adjusters is generally located on the drive-side end of the camshaft. It is comprised of a crankshaft-fixed drive wheel, a camshaft-fixed driven element, and an adjustment mechanism transmitting the torque from the drive wheel to the driven part. The drive wheel can be constructed as a chain, belt, or gearwheel and is locked in rotation with the crankshaft by means of a chain, belt, or gearwheel drive. The adjustment mechanism can be operated electromagnetically, hydraulically, or pneumatically. Mounting the camshaft adjuster on an intermediate shaft or supporting it on a non-rotating component is similarly conceivable. In this case, the torque is transmitted via additional drives to the camshaft.
Electrically operated camshaft adjusters are comprised of a drive wheel, which is in driven connection with the crankshaft of the internal combustion engine, a driven part, which is in driving connection with a camshaft of the internal combustion engine, and adjustment gearing. The adjustment gearing involves a triple-shaft gear mechanism, with three components rotating relative to each other. Here, the first component of the gearing is locked in rotation with the drive wheel and the second component is locked in rotation with the driven part. The third component is constructed, for example, as a toothed component, whose rotational speed can be regulated via a shaft, for example, by means of an electric motor or a braking device.
The torque is transmitted from the crankshaft to the first component and from there to the second component and thus to the camshaft. This happens either directly or under intermediate connection of the third component.
Through suitable regulation of the rotational speed of the third component, the first component can be rotated opposite the second component and thus the phase position between the camshaft and crankshaft can be changed. Examples for such triple-shaft gear mechanisms are internal eccentric gear mechanisms, double-internal eccentric gear mechanisms, shaft gear mechanisms, swashplate gear mechanisms, or the like.
For controlling the camshaft adjuster, sensors detect the characteristic data of the internal combustion engine, for example, the load state, the rotational speed, and the angular positions of the camshaft and crankshaft. This data is fed to an electronic control unit, which controls the adjustment motor of the camshaft adjuster after comparing the data with an engine-map range of the internal combustion engine.
From DE 100 38 354 a device for modifying the control times of an internal combustion engine is known, in which the torque transmission from the crankshaft to the camshaft and the adjustment process are realized by means of a swashplate gear mechanism. The device shown in FIG. 2 essentially comprises a drive wheel, a housing, a drive conical gearwheel, a camshaft-fixed driven element, and a swashplate. The drive wheel is in driven connection with a crankshaft and is constructed in one piece with the housing and the drive conical gearwheel. The housing, the drive conical gearwheel, and the driven element form a ring-shaped hollow space, in which the swashplate is arranged. The swashplate is supported at a defined contact angle on an adjustment shaft and is provided with a toothed ring on both axial side surfaces. Furthermore, the axial side surfaces of the drive conical gearwheel and the driven element facing the swashplate are likewise provided with a toothed ring. The toothed rings of the swashplate engage in the corresponding toothed rings of the drive conical gearwheel and the driven element. Here, the engagement takes place only within an angle segment, wherein the size of the angle segment is dependent on the contact angle of the swashplate. The torque of the crankshaft is transmitted via the drive wheel, the housing, the drive conical gearwheel, the swashplate, and the driven element to the camshaft.
The toothed rings of at least one gearing pair have different numbers of teeth.
The adjustment shaft is in driven connection with a drive unit, for example, an electric motor, which can drive this with continuously variable rotational speeds. Rotating the adjustment shaft relative to the driven element leads to a wobble rotation of the swashplate and thus to a rotation of the engaged angle segment relative to the drive conical gearwheel, the driven element, and the swashplate. Due to the different numbers of teeth of the conical gearwheel gearing, this leads to a relative rotation of the camshaft with respect to the crankshaft.
Lubricant is fed to the swashplate gearing, which has the task of reducing the friction, the wear, and the development of noise in contact positions with relative motion, for example, tooth contacts, sliding or cylinder bearings. Foreign particles can enter into the device with the lubricant and collect in the device. The foreign particles can involve, for example, original contamination of the internal combustion engine or rubbed-off metal particles produced during the operation of the internal combustion engine. Here, the foreign particles can find their way to the contact points with relative motion and damage the device.